1. Field of the Invention
The present invention relates to coded tagging of substances and more particularly, to a novel technique and system for identifying the source of oil spills and slicks.
2. Description of the Prior Art
There are several current serious situations which require improved means for identifying the vendors of certain materials. For example, certain ethical drugs are being overproduced and are finding their way into the illicit drug traffic. There is also a need to regulate and control the sale of explosives and ammunition. A most serious enforcement problem concerns the ability to identify the source of oil spills which are occuring at an ever increasing rate. Without the threat of prosecution of offenders by regulating agencies, the prospects of diminishing these activities are poor. The present analytical techniques are not sufficiently precise and exacting to stand the test of forensic attack.
According to the U.S. Coast Guard, in 1968 there were 714 major oil spills reported in U.S. waters. The problem of oil pollution is currently serious and is expected to grow more so with time. Oil pollution is illegal under at least six statutes of the U.S. code. One of the major problems in combatting oil pollution is to identify the polluter. Rapid and accurate identification of an oil spill out only aids in the forensic identification of the polluter, but can be of great value protecting those companies which have made significant efforts to improve their oil handling techniques. There are about 2,000 tankers making about 10,000 calls a year on U.S. Ports, with only 400 of these tankers flying the American flag. The international aspects compound the forensic problem, and the least that modern technology might contribute is in the providing of a rapid and accurate identification of the polluter.
Currently there are several techniques which have been proposed for the identification of oil spills which involve both passive tagging and active tagging.
Passive tagging is useful when the oils in a region of interest are so chemically diverse and so stable in the spill environment that a chemical fingerprint can be accurately determined in an analytical chemical laboratory. Techniques of passive tagging include (1) identification of heavy hydrocarbon fingerprint, (2) identification of trace metals such as vanadium and nickel and (3) identification of various sulfur-isotopic ratios. Less than half of the several hundred compounds appearing in any crude oil have yet to be identified. Due to rapid evaporation of the light fractions, photochemical oxidation, microbial oxidation, etc., passive tagging by means of the heavy hydrocarbons is quite limited in its usefulness. The usefulness of the trace metal passive tags is also severely limited because the associated inorganic compounds are generally soluble in water, and the associated organic compounds (vanadyl and nickel porphyrins) rapidly decompose when irradiated with ultraviolet radiation from the sun in the presence of oxygen.
Concerning the sulfur-isotopic ratio technique, unfortunately the isotopic ratios are known to be a general index of geological age and thereby not necessarily of location. Some of the isotopic ratios of Texas crude and Ontario crude, although separated by several thousand miles, are quite similar. Furthermore, the sulfur in oil is in a reduced state, but when spilled at sea begins to oxidize. Unfortunately, the compounds containing S-34 isotope, are more quickly oxidized than those containing the S-32 isotope, thus adding more uncertainty to the identification. Also microbial degradation results in fractionation of the lighter isotope.
Some authorities have recommended a combination of analytical techniques such as gas-liquid chromatography, controlled pyrolysis, mass spectrometry and computer calculations. In view of the above mentioned problems, it is believed that even a combination of these brute-force methods will be expensive and valueless.
The techniques of active tagging appear to be much more useful than those of passive tagging. Active tagging involves a coded material which is added to the oil. An ideal active tag would satisfy the following 10 criteria.
1. It must be an unusual material that is never found in the environment and is found only in the petroleum to which it has been added.
2. It must be compatible with (i.e., chemically unreactive and physically stable) and soluble or dispersible in the oil.
3. It must be both insoluble and nondispersible in water.
4. It must be relatively non-volatile.
5. It must be stable to chemical, photochemical, and microbial degradation in the oil-slick environment.
6. It must be easily detectable in extremely small quantities by readily available analytical techniques.
7. It must permit modifications so that when it is added to a particular oil shipment it provides a unique code or "license plate" for that carrier or transporter.
8. It must remain with the oil during the course of its history following a spill, and should then disappear from the surface.
9. It must in no way interfere with the end-use applications for that oil, nor complicate further processing and refining.
10. It must be available in quantity at economical prices.
Three techniques of active tagging are currently being tested. Techniques of active tagging include the use of (1) halogenated aromatic compounds identified with electron-capture gas chromatography, (2) organometallic compounds identified with standard spectroscopic methods, and (3) microspheroidal particles identified by size.
The organometallic tags include cyclohexanebutyrates and/or ethylhexanoates of Al, Ba, B, Cd, Ca, Cr, Co, Cu, Fe, Pb, Li, Mg, Mn, Hg, Ni, P, K, Si, Ag, NA, Sr, Sn, V and Zn. These compounds are stable, nonvolatile, oil soluble and are well characterized by a standard technique, emission spectroscopy. However, they can only be detected spectrographically in only about 1 part per million. Thus, one gram is needed per ton and at present the cost to tag a large tanker would be prohibitive.
There are other disadvantages to the use of these compounds. Only relatively few of the compounds are soluble in oil which limits the number of potential tags. Furthermore, most crude oils already contain many trace metals and microbial organisms are known to selectively accumulate certain trace metals.
The use of solid microspheroidal particle tags involves the use of well-characterized particles generally with diameters between 10-50 microns. There are several advantages of this tagging method. Only about 10.sup.3 particles/liter are needed. Thus with 10 micron particles only about 250 grams would be needed for a 500,000 ton tanker. Microspheroidal particles can be obtained in at least 11 distinct sizes between 10-50 microns in diameter and in at least 11 distinct density ranges between 0.9 and 1.5 grams/cm.sup.3. A variety of materials can be made into microspheroids: metals, ceramics, nitrides, carbides, celluloses, starches, polystyrene, phenolic resins, and many organics. The particles can easily be separated from the oil-slick samples.
However, crude oil already contains particulate matter such as spores, pollens, microalgae, etc. which could interfere with or complicate the separation and characterization of the tag. Furthermore, the microsphere could undergo oxidation or microbial attack under the oil-spill environment.
The halogenated aromatics do not naturally occur in crude oil. Polynuclear hydrocarbons are more stable to oxidation than aliphatic compounds and halogenation decreases volatility. Many possible sites for substitution of the four halogens provide a large number of different compounds. The tag compounds are identifiable by electron capture G.C. in amounts as low as 10.sup..sup.-12 grams.
However, relatively little is known about the stability of many of these compounds. The tag is chromatographed along with the oil slick giving rise to the possibility of interfering or overlapping with the tag's peak. It is possible that long after the peak has decomposed, that these relatively non-volatile compounds will persist, polluting the oceans surfaces and being entrained into new spills. Other compounds, such as polynuclear aromatic hydrocarbons, chlorinated biphenyls and pesticide residues all of which are present in the environment also give large signals in the electron capture detector.